1. Field of the Invention
The present invention relates to a mobile communication terminal, and more particularly, to an apparatus and method for controlling power consumption of the backlight control unit of a mobile communication terminal.
2. Description of the Related Art
In general, a mobile communication terminal is a device the size of which is limited to facilitate ease of carrying and use. Most users of mobile communication terminals favor compact terminals.
Generally, mobile communication terminals are powered, for example, by batteries which are charged by a charging unit that is not carried with the terminal. That is, users carry the mobile communication terminal without the charging unit. Therefore the time of use of the terminal is limited by the charge of the battery.
There are two ways to extend the time of use before the mobile communication terminal must be returned to the charging unit. A larger capacity battery may be mounted in the terminal. Alternately, power consumption of the battery may be reduced.
Increased battery capacity generally requires a larger battery. A larger battery in the terminal would not meet users' demand for a more compact terminal. Therefore, manufacturers attempt to minimize power consumption of the battery.
As the use of mobile communication terminals having a liquid crystal display (LCD) has increased, the use of a backlight at the rear side of the LCD panel in order to illuminate the LCD has increased. The backlight is generally battery-driven.
FIG. 1 illustrates a conventional backlight control unit 1 of a mobile communication terminal. As illustrated in FIG. 1, the backlight control unit 1 includes a voltage source such as a battery (not shown), a converter 10, a backlight illumination unit 20 driven by power from the converter 10, and a backlight power switch 30.
The converter 10, for example a charge pump or DC-DC converter, converts the voltage (VBATT) of the battery to a constant DC voltage (V_BACK). A backlight enable signal (LCD_BACK_EN) controls application of the constant DC voltage to the backlight illumination unit 20.
The backlight illumination unit 20 includes LEDs (LED1, LED2 and LED3) connected in parallel to emit light for illuminating the LCD and resistors (R1, R2 and R3) connected in series to each LED for controlling current. The backlight power switch 30, for example a transistor (Q1), turns a current flowing to the backlight illumination unit 20 on and off according to the backlight enable signal (LCD_BACK_EN).
The battery voltage (VBATT) generally varies between 4.2 VDC and 3.0 VDC as battery power is consumed. If such a voltage were used to power the backlight illumination unit 20, the brightness of the LEDs would also vary, thereby causing the illumination of the LCD to vary. In order to prevent such varying illumination, the converter 10 is used to provide a constant DC voltage (V—BACK) and, hence, consistent illumination of the LCD.
When a CPU (not shown) generates the backlight enable signal (LCD_BACK_EN), the converter 10 and the backlight power switch 30 are turned on. The constant DC voltage (V_BACK) from the converter 10 is applied to the backlight illumination unit 20 and current flows through the backlight power switch 30 through the LEDs (LED1, LED2 and LED3) and the resistors (R1, R2 and R3). The LEDs emit light and the LCD is illuminated.
In order to provide a constant DC level, the converter 10 operates as a down-converter when the voltage (VBATT) of the battery is equal to or above a reference voltage, for example 4V, and operates as an up-converter when the voltage of the battery is below the reference voltage. In this manner, the converter 10 outputs a constant 4.0 VDC (V_BACK) regardless of the change in the voltage level of the battery (V_BATT). However, a typical converter 10 has efficiency below 90%. Therefore, 10% or more of battery voltage is unnecessarily wasted and available use time for the terminal 1 is decreased.
Therefore, there is a need for an apparatus and method that can control the application of power to the backlight illumination unit for an LCD display of a mobile communication terminal in a manner that reduces power consumption of the backlight control unit. The present invention meets these and other needs.